Abstract

This study assessed medial translation of the hip joint achieved by the Bernese periacetabular osteotomy (PAO) in correcting residual acetabular dysplasia deformities. 86 hips in 75 patients with an average age of 25 years (range, 12-50) were treated for symptomatic acetabular dysplasia with a periacetabular osteotomy. Radiographic analysis was performed to assess correction of the acetabular deformity with specific attention to the horizontal position of the hip joint center. All hips were followed until bony union of the iliac osteotomy and the average follow-up was 28 months. The lateral center edge angle improved an average 31.6° (-0.4° preoperative, 31.2° at follow-up). Anterior center edge angle improved 39.3° (-4.5° to 34.8°). The acetabular roof obliquity improved an average 21.8° (25.1° to 3.3°). Preoperatively, the average distance from the medial aspect of the femoral head to the ilioischial line was 17.6 mm. This distance was decreased to an average 7.8 mm postoperatively. This change resulted in an average medial translation of the hip joint center of 9.8 mm, (range -6 to 31mm). Overall, some degree of medial translation of the hip joint center was obtained in 79 (92%) of the hips. 4 (5%) were maintained in the same horizontal position, and 3 (3%) had slight lateral repositioning. For the hips translated medially, the average change was 10.0 mm, and 72% of all hips had an optimal correction with the distance between the medial aspect of the femoral head and the ilioischial line being between 0 and 10 mm. This study demonstrates that in addition to optimizing femoral head coverage, a major and distinct advantage of the periacetabular osteotomy is reproducible and consistent medial translation of the hip joint center.

INTRODUCTION

Residual acetabular dysplasia is a complex, multiplanar deformity of the acetabulum that is characterized by deficient anterior and lateral femoral head coverage, superolateral inclination of the acetabular joint surface and a relative lateral position of the hip joint center10,28. The total articular surface area of the dysplastic acetabulum is reduced and version of the acetabulum may also be abnormal. Ideally, the goal of reconstructive osteotomy surgery is to correct all aspects of hip dysplasia which includes both acetabular reorientation and medial translation of the hip joint center. Medial translation is emphasized because it optimizes hip function by decreasing the gravitational lever arm, and therefore decreasing the joint reaction force1,2. Theoretically, this may enhance the longevity of the surgically corrected pre-arthritic or early arthritic hip.

A variety of pelvic osteotomies have been developed in order to address the deformities of the dysplastic acetabulum. These have included single17, double22, triple8,21,23, and spherical osteotomies5,16,27. The majority of these reconstructive techniques are limited in achieving consistent medial translation of the hip joint center, and major medial repositioning is not possible with some of these techniques. In contrast, the Bernese periacetabular osteotomy4,10,14,20,19,25 enables major, multiplanar deformity corrections, including medial translation of the joint center. Nevertheless, there is limited literature describing the reproducibility and magnitude of medial translation of the hip joint achieved with the Bernese periacetabular osteotomy. The purpose of this study was to analyze our first 86 consecutive periacetabular osteotomies to assess acetabular reorientation and medial translation of the hip joint center achieved with this osteotomy.

MATERIALS AND METHODS

Radiographic assessment was performed on 86 consecutive periacetabular osteotomies in 75 patients treated by the senior authors. All patients were treated at our institution hospitals and this group of patients represents our learning curve experience. There were 52 (58 hips) female patients and 23 (28 hips) male patients. The average age of the patients was 25 years (range, 12 to 50 years). All patients were skeletally mature at the time of surgery and had symptomatic acetabular dysplasia. Three patients had treatment during infancy with closed reduction and casting and five patients had open reduction and casting. Five patients had previous pelvic osteotomy surgery and four had previous femoral osteotomy surgery. Preoperative evaluation demonstrated a radiographically congruent hip joint and adequate range of motion to tolerate reorientation of the acetabulum. No patient had advanced osteoarthritis.

All osteotomies were performed on a radiolucent table. Intraoperative fluoroscopy was used to direct the osteotomy cuts and to assess acetabular reduction intraoperatively. Cell saver and spontaneous EMG monitoring were utilized throughout the procedure. The modified anterior15 or the modified Smith Petersen approach10,12 were used in all cases. A standard sequence of periacetabular cuts was performed as previously described4,10. Acetabular reduction was then achieved by first translating the acetabulum medially. After adequate medial translation was obtained, the acetabulum was reoriented to achieve lateral coverage, anterior coverage, and maintain or obtain anteversion of the acetabulum. The osteotomy was then provisionally fixed with K-wires, and the acetabular reduction was assessed intraoperatively with fluoroscopy. Definitive acetabular fragment fixation was performed with 4.5 mm screws in the majority of cases and pelvic reconstruction plate fixation in selected cases. At the time of provisional acetabular reduction and after definitive fixation, we assessed lateral coverage of the femoral head, anterior coverage of the femoral head, the inclination of the acetabular joint surface, medial translation of the hip joint center, and version of the acetabulum. Care was taken to avoid excessive leg lengthening and over correction of the acetabulum anteriorly.

Postoperatively, patients were treated with 30 pounds, partial weight bearing, and no active hip flexion for six weeks. Over the following month, 50% weight bearing was allowed, with full weight bearing permitted at ten weeks postoperatively. Strengthening exercises were initiated six weeks postoperatively. Patients were gradually progressed to independent ambulation on an individual basis.

Radiographic analysis of these cases was performed by two of the authors (JCC, SEB). Standing AP and false profile views were assessed for all patients. These included preoperative, immediate postoperative, and final follow-up radiographs. Lateral center-edge angle28, anterior center-edge angle9, acetabular roof obliquity11, and the hip joint center position in the vertical and horizontal planes were measured. The vertical position of the hip was determined by measuring the distance from a line drawn between the ischial tuberosities and the superior margin of the lesser tuberosities. The change in horizontal position of the hip center was determined by measuring the distance between the ilioischial line and the medial aspect of the femoral head (Figures 1 and ​and2).2). The distance measured postoperatively was subtracted from the preoperative distance to determine the change in the horizontal and vertical positions of the hip joint. Medial translation of the hip joint center was calculated by determining the relative position of the hip joint center on preoperative and postoperative radiographs. A change was considered significant if it demonstrated a difference greater than 2 millimeters. Osteotomy union was also assessed radiographically. Pre-operative values for all variables were compared to post-operative values using a Student's t-test.

Preoperative (1a) and two year postoperative (1b) anteroposterior pelvic radiographs of an 18 year old female treated with a periacetabular osteotomy for symptomatic acetabular dysplasia. Medial translation of the hip center is demonstrated by the change...

Preoperative (2a) and five year postoperative (2b) anteroposterior radiographs of a thirteen year old female with severe acetabular dyplasia and lateral femoral head subluxation. Major (15mm) medial translation of the hip joint was achieved in this case...

RESULTS

Radiographic analysis was completed on all 86 hips in 75 patients. All hips were followed to bony union of the ilium and the average radiographic follow-up was 28 months (range, 13 to 62 months). No hips were lost to follow-up. Overall, radiographic corrections are summarized in Table 1. The lateral center edge angle improved from the preoperative average of -0.4° to a postoperative average of 31.2°. Anterior center edge angle improved from an average -4.5° to 34.8° postoperatively. The acetabular roof obliquity improved from 25.1° preoperatively to 3.3° postoperatively. The average distance from the most medial aspect of the femoral head to the ilioischial line on preoperative radiographs was 17.6 mm. This value decreased to an average 7.8 mm after surgery. Therefore, the average hip joint center was translated medially an average of 9.8 mm. All of these radiographic changes comparing preoperative and postoperative measurements were significant at p<0.0005. Seventy-nine of 86 hips (92%) had some degree (>2mm) of medial translation, while four (5%) maintained the same horizontal position. Three hips (3%) had slight lateral repositioning not according to the preoperative plan. Sixty-two (72%) had an optimal correction with the postoperative distance between the ilioischial line and the medial aspect of the femoral head measuring between 0 and 10 mm. Inferior displacement of the hip center averaged 4.0 mm.

DISCUSSION

Various osteotomies have been designed to address the complex deformities associated with acetabular dysplasia1,4,5,8,16,17,21,22,23,27. For example, the Chiari osteotomy is a salvage procedure designed to enhance femoral head coverage with nonarticular fibrocartilage. In Chiari's original work, he emphasized the importance of decreasing the lever arm of the hip abductors in the lateral plane as a goal of osteotomy surgery1. Since that time, many osteotomies have been described, each with a varying ability to normalize joint biomechanics and correct the multiple associated deformities of the dysplastic hip. Hogh et al. reported on their results following 94 Chiari osteotomies in 81 patients6. Medial displacement was measured as the percentage of displacement of the acetabular side of the osteotomy from its original location. In this study, the osteotomy was translated an average of 68% of the width of the ilium. However, by measuring the horizontal distance from the medial aspect of the femoral head to the most inferior point of the teardrop, he noted an average of 1 mm of lateral subluxation of the femoral head within the acetabulum. Therefore, while the hip joint center is displaced medially, the actual position of the femoral head within the acetabulum may be inconsistent. Kubo evaluated changes in hip center position using CT scans before and after Chiari osteotomies in 23 patients7. He documented an average medial displacement of the center of the hip joint of 6 mm. Therefore, these studies support the feasibility of medial translation of the hip joint center with the Chiari osteotomy. Nevertheless, despite some ability to achieve medial translation, the major weakness of the Chiari procedure is lack of femoral head coverage with articular hyaline cartilage. Rather, coverage is achieved with metaplastic fibrocartilage, which is suboptimal.

Salter described his innominate osteotomy as a treatment for hip dysplasia in both children and adults. In this procedure a single osteotomy allows the surgeon to rotate the acetabulum to improve both anterior and lateral coverage of the femoral head17. In our review of the literature, we found no studies which documented medial translation achieved with Salter's innominate osteotomy. Therefore, while the innominate osteotomy may theoretically improve on the Chiari, by maintaining the congruity of the hip joint and enhancing articular cartilage coverage, the ability to reliably translate the hip joint medially, to our knowledge, has not been established.

Double and triple innominate osteotomies have also been employed in the treatment of acetabular dysplasia. Sutherland and Greenfield acknowledged the benefit of medial displacement in reconstructive pelvic osteotomy and proposed that one advantage of the double osteotomy over the Salter innominate osteotomy is the ability to translate the hip center toward the midline. They reported their results on 25 patients in whom they performed the double innominate osteotomy22. This procedure began with the iliac osteotomy described by Salter, but was then followed by a second osteotomy placed medial to the obturator foramen between the pubic tubercle and the symphysis pubis. Radiographic follow-up revealed an average measurement of 15 mm of medial translation22. In terms of medial translation of the hip, their data clearly improve on the correction obtained by the single osteotomy. Additionally, Steel proposed a triple innominate osteotomy with the intention of further improving the ability to correct the multiplanar deformity associated with developmental dysplasia of the hip21. Frick et al. reported on seven patients who underwent CT scanning before and after triple innominate osteotomy3. While these patients represented more complex cases which the authors felt required pre-operative CT evaluation, no significant change in horizontal position of the hip was found after surgery. Despite its small sample size, this study describes a decreased ability to reliably translate the hip joint center with a triple innominate osteotomy. These results reflect inherent difficulties in controlling the correction of a multiplanar deformity with a relatively large acetabular fragment that can be tethered with muscular and ligamentous attachments. Nevertheless, it should be noted that the Tönnis triple innominate osteotomy23 may provide medial translation as the inferior osteotomy is superior to the sacrospinous ligamentous attachment which may facilitate acetabular repositioning.

Another class of osteotomies have been proposed and evaluated in terms of deformity correction in dysplastic hips. Wagner introduced the spherical osteotomy27, and subsequently described the Type III modification of his original osteotomy. This Type III osteotomy was intended for treatment of patients with dysplasia characterized by lateralization of the hip center. In such cases, he performed his original spherical osteotomy, and then displaced the hip center medially via a combined Chiari osteotomy. Unfortunately, to our knowledge no data have been reported on the actual medial translation achieved by adding this modification to the procedure. His work does, however, reinforce the biomechanical principles of hip joint preservation by reduction in joint reactive force acting on the hip.

Nakamura, et al. reported on 97 patients in whom they performed a rotational acetabular osteotomy16. They found an average medial displacement of 7 mm measured from the medial border of the femoral head to the ilioischial line. In their study, 58 of 97 patients were optimally corrected, defined as translation of the hip 2.5 to 12.5 mm medial to its starting position. They achieved no change in the horizontal direction in 22 patients (22%). Twelve patients were overcorrected, defined as translation more than 12.5 mm, while 5 hips moved more than 2.5 mm in the lateral direction. Based on their criteria, 58% of patients were optimally corrected with respect to medial translation of the hip joint center.16 Thus, the rotational acetabular osteotomy does enable medial translation in the majority of cases.

In attempts to improve on the rotational osteotomy, Hasegawa et al. describe an eccentric rotational osteotomy, which maintains all of the benefits of the spherical osteotomies, but also adds the ability to translate the hip center toward the midline. They performed the procedure on 132 hips and found an average medial displacement of 4.1 mm5. While this data is promising, the amount of medial translation achieved appears to be less than that afforded by the PAO, and the operation is technically more demanding. Sotelo-Sanchez et al., in a recent review, state that the spherical osteotomies are limited in translating the hip joint center medially18, since the medial aspect of the quadrilateral plate remains intact with these osteotomies.

Since its description4, the Bernese periacetabular osteotomy has gained favor in terms of its ability to improve the acetabular position in multiple planes. Siebenrock et al. reported on their first 75 procedures in 63 patients and demonstrated an average correction of 6 mm of medial translation of the hip joint20. Other investigators12,1314242526 have also reported that, in general, medial translation of the acetabulum can be achieved with the periacetabular osteotomy. Nevertheless, the magnitude of correction and the reproducibility of medial translation has not been emphasized in the literature. Our data, collected from our learning curve experience, indicate that medial translation can be achieved consistently with this technique. Specifically, we obtained an average 9.8 mm of medial translation in our cases. Perhaps, more importantly, some degree of medial translation was obtained in 92% of hips and 72% were thought to have an optimal correction. Thus, in addition to major corrections of anterior and lateral femoral head coverage, reliable medial translation of the hip joint is a distinct advantage of the Bernese periacetabular osteotomy. This advantage is most notable in severely dysplastic hips with major lateral subluxation (Figure 2).

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